Conventionally, a sheet article such as a document or a photo is usually covered with a protective film for protection because such a sheet article is readily suffered from damage. Generally, the sheet article is clamped between two films (i.e. thermoplastic films), and then sealed between these two films by a sheet laminating apparatus in order to achieve the protective purpose.
Hereinafter, the configurations of a conventional sheet laminating apparatus will be illustrated with reference to FIG. 1. FIG. 1 is a schematic side view illustrating a conventional sheet laminating apparatus. As shown in FIG. 1, the sheet laminating apparatus 1 comprises a heat-treating member 10, a conveying and laminating roller 11 and a transfer passage 12. The heat-treating member 10 comprises an electrically-heated plate 101 and a heater 102. The operations of the sheet laminating apparatus 1 will be described as follows. Firstly, a sandwich structure of an article sheet (not shown) intervening between two films (not shown) is fed to the conveying and laminating roller 11 through the transfer passage 12. By means of the conveying and laminating roller 11, the article sheet and the two films are continuously transported through the passage 12. During this stage, the electrically-heated plate 101 of the heat-treating member 10 transforms electricity to heat energy. The heat energy is uniformly distributed by the heater 102 and radiated through an air gap so as to heat up the conveying and laminating roller 11. The heated conveying and laminating roller 11 performs a hot pressing operation (i.e. a laminating operation) on the sandwich structure that is transported through the transfer passage 12. As such, the two films are softened by the heat energy in the transfer passage 12. After being transmitted and pressed by the conveying and laminating roller 11, the sheet article bonds with the softened films to form a laminated structure, and thus the sheet article is fixed between these two films. Afterwards, the laminated structure is transported across the transfer passage 12 and withdrawn from the sheet laminating apparatus 1, and the laminating operation is completed.
Although the conventional sheet laminating apparatus 1 is able to laminate the sheet article and the films, the conventional sheet laminating apparatus 1 may incur some problems if the thicknesses of the sheet article and the films are too large. FIG. 2 is a schematic side view illustrating the use of a conventional sheet laminating apparatus to laminate two films and a sheet article. For example, for laminating a thick sheet article D and two thick films S1 and S2, the sheet article D and the two films S1 and S2 are transported across the transfer passage 12 and then introduced into a region between two conveying and laminating rollers 11. At this moment, since the overall thickness of the sheet article D and the two films S1 and S2 is greater than the spacing interval between the two conveying and laminating rollers 11, the sheet article D and the two films S1 and S2 are sustained against the conveying and laminating rollers 11 to move the conveying and laminating rollers 11. That is, the upper conveying and laminating roller 11 (see FIG. 2) is moved upwardly, and the lower conveying and laminating roller 11 (see FIG. 2) is moved downwardly. As known, during the process of moving the conveying and laminating rollers 11, the conveying and laminating rollers 11 are readily collided with the high-temperature heaters 102. In this circumstance, the conveying and laminating rollers 11 are possibly damaged by the high-temperature heaters 102.
For preventing the sheet article and the two films from being sustained against the conveying and laminating rollers to result in collision between the conveying and laminating rollers and the heaters, some commercially available sheet laminating apparatuses are designed to increase the spacing interval between the conveying and laminating roller and the heater. Although the increase of the spacing interval between the conveying and laminating roller and the heater may avoid the collision between the conveying and laminating roller and the heater, some new problems occur. For example, since the spacing interval between the conveying and laminating roller and the heater is increased, the loss of the heat energy is increased and the heating efficiency of the sheet laminating apparatus is usually insufficient. In other words, the time period of delivering heat energy to the conveying and laminating roller is prolonged.
Therefore, there is a need of providing an improved sheet laminating apparatus in order to enhance the heating efficiency and reduce the damage of the conveying and laminating roller from collision.